Glass materials have been used in application fields such as lenses, prisms, optical filters, mobile devices, and display devices. In these application fields, the substitution of such glass materials with resin materials has been actively considered. Among them, curable resin materials that have excellent heat resistance (thermal stability) and strengths receive attention and are increasingly applied to a variety of uses. Under these circumstances, there is a need for curable resin materials excellent in all required properties such as curability, heat resistance (glass transition temperature), and mechanical strength.
Of the curable resin materials, cycloaliphatic epoxides are exemplified as materials having excellent curability, and a variety of ways has been attempted to allow cured products of the cycloaliphatic epoxides to have still better heat resistance (higher glass transition temperature) and/or higher mechanical strength. In a considered way so as to allow a cured product to have higher mechanical strength, a glycidyl-containing compound and/or an oxetanyl-containing compound is incorporated into a cycloaliphatic epoxide. In general, however, the resulting material has inferior curability upon the incorporation of a glycidyl-containing compound. The resulting material gives a cured product having a lower glass transition temperature upon the incorporation of an oxetanyl-containing compound, although the material exhibits better curability. It is difficult to improve the mechanical strength while maintaining the curability and the glass transition temperature at satisfactory levels.
Independently, a variety of attempts have been made to use silicone materials in curable resin materials so as to allow the materials to have better properties. Typically, a known curable composition includes a silicone material, an organic compound, a hydrosilylation catalyst, and fine polymer particles. The silicone material is a compound containing at least two SiH groups per molecule. The organic compound has a triallyl isocyanurate structure and contains carbon-carbon double bonds that are reactive with the SiH groups (see Patent Literature (PTL) 1). A known thermosetting resin composition includes a polysiloxane, an aromatic-ring-containing epoxy resin, and a curing agent. The polysiloxane contains a reactive cyclic ether group and contains D units and T units in a random form. The D units are derived from an aromatic-ring-containing dialkoxysilane. The T units are derived from a trialkoxysilane containing a a reactive cyclic ether group (see PTL 2). Independently, a known optical resin composition includes a silsesquioxane derivative, an alicyclic-skeleton-containing epoxy resin, and a curing agent and gives an optical component having an Abbe number 55 of or more. The silsesquioxane derivative has a random structure and/or a ladder-like structure (either one or both of a random structure and a ladder-like structure) and is obtained by hydrolytically condensing an alkyl- or aryl-containing trialkoxysilane with an epoxy-containing trialkoxysilane (see PTL 3).
All the citations, however, fail to disclose a way to allow a composition to give a cured product having higher mechanical strength while maintaining excellent curability of the composition and a high glass transition temperature of the cured product.
Recent electronic products have had dramatically decreasing size and weight and dramatically increasing performance. Such electronic products are represented by mobile phones, smartphones, tablet terminals, mobile computers, personal digital assistants (PDAs), and digital still cameras (DSCs). With the technological trend, demands have been increasingly made to reduce the size, weight, and thickness of lenses for use typically in cameras to be mounted to these electronic products. To meet the demands, wafer-level lenses have been used increasingly.
Imagers typically of cameras have an increasing number of picture elements. This necessitates lenses having such a high resolving power as to support the increasing number of picture elements and employs, for example, cemented lenses each including a stack of two or more lenses. The wafer-level lenses are suitable for such uses. In general, lenses have different refractive indices for different wavelengths of light and undergo chromatic aberration. The chromatic aberration is a phenomenon in which displacements (halation or blur) occur in the image. To reduce the influence of the chromatic aberration, regular lenses have a structure in which a lens having a high Abbe number is used in combination with a lens having a low Abbe number to compensate the chromatic aberration. Of lens glass for use in cameras, glass having an Abbe number of 50 or less and glass having an Abbe number of 50 or more are respectively called flint glass and crown glass.
As materials for the wafer-level lenses, curable resin materials that have excellent heat resistance and strengths receive attention. To efficiently produce high-quality wafer-level lenses, demands are made to provide curable resin materials that excel in all of curability, heat resistance (e.g., a glass transition temperature), and mechanical strength. Curable resin materials, if being inferior in any of these properties, may adversely affect the quality and/or productivity of the resulting wafer-level lenses. For example, a curable resin material having poor curability requires a long time to undergo a molding process and suffers from inferior productivity. A curable resin material having a low glass transition temperature suffers typically from sagging and causes the resulting lens to have inferior shape precision (dimensional precision). A curable resin material having a low mechanical strength suffers from cracking upon releasing from the mold.
The curable resin materials are exemplified by epoxides that excel typically in electrical properties, water-vapor resistance, and heat resistance. Among them, cycloaliphatic epoxides are materials excellent typically in electrical properties, water-vapor resistance, heat resistance, transparency, and curability and are suitable particularly in molding (forming) of wafer-level lenses. Typically, in a known technique, an organic-inorganic composite resin composition is used so as to give a cured product that has excellent heat resistance and less suffers from heat discoloration due to heating and deterioration in mechanical strength (see PTL 4). The organic-inorganic composite resin composition includes an organic resin component (e.g., a cycloaliphatic epoxide) and an inorganic fine particle component. Although in a known transparent encapsulating material, a cycloaliphatic epoxide is preferably used so as to give a cured product having a higher glass transition temperature (see PTL 5).
Various attempts have been made to allow cured products of curable compositions including a cycloaliphatic epoxide to have still higher glass transition temperatures and/or still higher mechanical strength. Typically, incorporation of a glycidyl-containing compound, an oxetanyl-containing compound, or a silicone compound into a cycloaliphatic epoxide has been attempted. Typically, a known curable composition includes a silicone material, an organic compound, a hydrosilylation catalyst, and fine polymer particles (see PTL 1). The silicone material is a compound containing at least two SiH groups per molecule. The organic compound has a triallyl isocyanurate structure and contains carbon-carbon double bonds that are reactive with the SiH groups. A known thermosetting resin composition includes a polysiloxane, an aromatic ring-containing epoxy resin, and a curing agent (see PTL 2). The polysiloxane contains a reactive cyclic ether group and contains D units and T units in a random form. The D units are derived from a dialkoxysilane containing an aromatic ring. The T units are derived from a trialkoxysilane containing a reactive cyclic ether group. Independently, a known optical resin composition includes a silsesquioxane derivative, an alicyclic skeleton-containing epoxy resin, and a curing agent and gives an optical component having an Abbe number 55 of or more (see PTL 3). The silsesquioxane derivative has a random structure and/or a ladder-like structure (either one or both of a random structure and a ladder-like structure) and is obtained by hydrolytically condensing an alkyl- or aryl-containing trialkoxysilane with an epoxy-containing trialkoxysilane.
Independently, a disclosed method for producing an optical element such as a lens includes producing an optical element wafer and cutting the optical element wafer to give pieces of optical elements (see PTL 6). In the method, the optical element wafer is produced by a method that includes the step of pressing or stamping an optical element material to a predetermined thickness using an upper stamper mold and a lower stamper mold. The optical element material is then cured by light or heat. Another disclosed method for forming an electronic element module includes forming an integrated assembly as a stack of two or more different optical element array plates (see PTL 7). The assembly is then cut at once to give chip sections to thereby give the electronic element module including a stack of two or more lenses. Each of the optical element array sheets includes two or more lenses arrayed in a matrix.
All the citations, however, fail to disclose a way to allow a material to maintain its high curability and to still give a cured product having higher mechanical strength and still having a high glass transition temperature as maintained. In addition, all the citations fail to describe a way to efficiently give a high-quality wafer-level lens as mentioned above.